1. Field of the Invention
The subject invention relates to a system for deploying the petals of a sectored mirror of an optical space telescope, and more particularly, to a set of hinges for independently connecting a petal of the sectored mirror to the central hub of the sectored mirror and to a latch mechanism for securing the hinged petal to the central hub in a deployed position.
2. Background of the Related Art
The success of the Hubble Space Telescope has spurred the development of other space-based astronomical observatories, including some incorporating a large diameter primary mirror. A number of designs, including the space-based observatory known as the Next Generation Space Telescope (NGST), have centered on a primary optic that is between six and eight meters in diameter.
Several problems must be overcome to realize a space-based astronomical observatory having such a large diameter mirror. For example, designs that propose a large diameter monolithic mirror would present significant manufacturing difficulties and risks. In addition, the size and shape of an observatory having a large diameter mirror would be constrained by the volume and shape of payload or cargo bays available on current launch vehicles.
Designs that propose a deployable large diameter mirror present other problems. For example, to achieve a desired surface accuracy and optical quality, the reflective components (e.g., sectors, segments or petals) of the mirror must be aligned to a very high degree of precision, such as, within about 10 nanometers. In addition, because the space-based observatory would experience broad thermal gradients, the thermal expansion and contraction of the deployable reflective components would need to be accommodated.
It would be beneficial therefore, to provide a deployment system for the reflective components of an optical space telescope that exhibits a high degree of precision and accommodates thermal changes experienced in an operational environment.
The subject invention is directed to a new and useful system for deploying the petals of a sectored mirror assembly of an optical space telescope. The mirror assembly includes a central hub and a plurality of petals disposed about the periphery of the central hub. Each petal has a petal root that is independently hinged to the central hub of the mirror assembly.
The petal deployment system of the subject invention includes a first hinge assembly having a root mount secured to a petal root and a hub mount secured the central hub. The first hinge assembly is adapted and configured to afford the petal associated therewith freedom of rotation about a petal hinge axis.
The petal deployment system further includes a second hinge assembly having a root mount secured to the petal root and a hub mount secured to the central hub. The second hinge assembly is adapted and configured to afford the petal associated therewith freedom of rotation about the petal hinge axis, as well as freedom to expand and contract thermally, and move rigidly along the petal hinge axis in a frictionless, unconstrained manner.
The petal deployment system further includes a latch assembly including a clevis secured to the petal root at a location spaced from the hinge axis and a pair of laterally opposed latches that are operatively associated with the central hub for engaging the clevis upon rotation of the petal about the hinge axis from a stowed position to a deployed position.
Preferably, the first hinge assembly includes a first hinge shaft disposed on the petal hinge axis. The first hinge shaft is secured to the root mount of the first hinge assembly, and supports a plurality of axially spaced apart angular contact bearings. The angular contact bearings are formed from silicon nitride, do not require lubrication and are housed within the hub mount of the first hinge assembly.
Preferably, the second hinge assembly includes a second hinge shaft disposed on the petal hinge axis. The second hinge shaft is supported by the root mount of the second hinge assembly, and is disposed within a cylindrical bearing cage. The bearing cage is formed from PTFE and retains a plurality of ball bearings. The ball bearings are formed from silicon nitride and do not require lubrication. The bearing cage is disposed between an inner bearing race and an outer bearing race, and is housed within the hub mount of the second hinge assembly.
Preferably, the latch assembly of the subject invention is adapted and configured to afford the petal associated therewith freedom to expand and contract thermally, and move rigidly along a latch axis extending parallel to the hinge axis in a frictionless, unconstrained manner. Each laterally opposed latch of the latch assembly includes a latch shaft mounted for linear movement along the latch axis. The clevis of the latch assembly defines a reception aperture for receiving the laterally opposed latch shafts, and an actuator is operatively associated with each latch for moving the latch shaft thereof into engagement with the clevis.
Each latch shaft is disposed within a cylindrical bearing cage, and each bearing cage is formed from PTFE. Each bearing cage retains a plurality of ball bearings formed from silicon nitride, and is disposed between an inner bearing race and an outer bearing race. Each bearing cage is housed within a hub mount secured to the central hub, and each hub mount includes a base portion and a cylindrical housing portion.
These and other unique features of the petal deployment system of the subject invention will become more readily apparent from the following description of the drawings taken in conjunction with the description of the preferred embodiment.